The Keystone State could be the key race in deciding which party controls the Senate next year.

Sen. Patrick J. Toomey gets high marks from GOP strategists for his re-election campaign so far in Pennsylvania and he’s received a few atypical endorsements for a GOP incumbent. But the weight of Donald Trump at the top of the ballot and the Democratic lean of the state is putting him in a precarious electoral position.

The Democratic Senatorial Campaign Committee spent big to get Katie McGinty through the primary. But she appears to be getting her sea legs, and is now running neck and neck with (and sometimes ahead of) the incumbent in general election polls.

Toomey’s critics say he was an ineffective co-sponsor of the background checks legislation, but the endorsements give the senator something tangible to point to as he tries to craft a bipartisan image.

Democrats are well-positioned to take over Senate seats in Illinois, Wisconsin, and Indiana. They could gain control of the chamber by winning Pennsylvania, if the party is also able to hold retiring Minority Leader Harry Reid’s seat in Nevada — and the White House, enabling a Democratic vice president to break a tie.

Meanwhile, in Colorado, Sen. Michael Bennet was once seen as the only Democratic senator the GOP had a chance of unseating this election season. But Republican challenger Darryl Glenn’s general election campaign has been slow to take off with recent polls showing him trailing Bennet by double digits.